The further development of a sensitive, reliable, convenient and easy mammalian (murine) host-mediated assay procedure using mammalian indicator cells for the detection of chemical mutagens. This test will consider host pharmacodynamic factors such as chemical activation, detoxification, storage and excretion and will allow the simultaneous comparison of point mutations, cytogenetic aberrations and biochemical parameters which indicate DNA damage, e.g., DNA repair mechanisms. The indicator cells are the L5178Y murine leukemia (ascites form). The assay is performed with the L5178Y murine leukemia cell which is implanted into the peritoneal cavity of BDF1 mice. Several days later the mice are treated with the chemical in question through a distal route. After a suitable expression period, the ascites cells are harvested and cloned in soft-agar to determine viability, induced mutation (reverse, L5178Y/asn minus to asn plus or minus and forward, L5178Y/asn plus to asn minus) and cytogenetic aberrations in the L5178Y and bone marrow stem cells. The L5178Y is also treated with the chemical in vitro and the same studies are performed. Comparison of in vivo and in vitro effects of the chemical indicate host effect on the chemical. Thus chemicals which are not mutagenic in in vitro assays may be very potent mutagens in the animal due to host activation. Conversely, rapid host metabolism or excretion may provide negative in vivo results when significantly positive results were obtained in vitro.